1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to improvement of dimples of a golf ball.
2. Description of the Related Art
Golf balls have numerous dimples on the surface thereof. Surface shape of general dimples is circular. A role of the dimples involves causing turbulent flow separation through disrupting the air flow around the golf ball during the flight. By causing the turbulent flow separation, a separating point of air from the golf ball shifts backwards leading to the reduction of a drag coefficient (Cd). The turbulent flow separation promotes the differentia between the separating points at the upper and lower sides of the golf ball, which result from the backspin, thereby enhancing the lift force that acts upon the golf ball. Flight distance of the golf ball is prolonged on behalf of the reduced drag and enhanced lift force. Aerodynamically excellent dimples promote the turbulent flow separation. In other words, aerodynamically excellent dimples can disturb the air flow more efficiently.
Specifications that greatly affect flight performances of a golf ball include density of dimples (also referred to as “occupation ratio”). Golf balls having a great density are excellent in flight performances. Various proposals have been made regarding the density. U.S. Pat. No. 4,813,677 discloses a golf ball provided with dimples that are densely arranged such that any new dimple having an area that is greater than the average area can not be formed.
Of the surface of a golf ball, a part other than dimples is referred to as a land. The land having a great area inhibits aerodynamic characteristics of the golf ball. When the plane shape of a dimple is circular, it is impossible to completely fill the surface of the golf ball with dimples. According to golf balls having circular dimples arranged thereon, a land having a certain area is inevitably generated.
Cross-sectional shape of a dimple has been contrived, and thus golf balls with a reduced land have been proposed. JP-A No. 7-289662 and JP-A No. 2003-47674 corresponding to the divisional application of the same disclose a golf ball with a reduced land area through the use of hexagonal dimples. U.S. Pat. No. 6,290,615 and U.S. Pat. No. 6,461,253 disclose golf balls having the surface thereof provided with lattice protrusions and concave portions, thereby reducing the land area.
Top concern of golf players for golf balls is the travel distance. In light of the improvement of travel distance, there remains room for improvement of the dimple. An object of the present invention is to improve the flight performance of a golf ball.